This invention relates to data imprinting devices for a camera, which can imprint and superpose on a picture to be photographed certain types of data, such as the date when the picture is taken. More particularly, the invention relates to a data imprinting device having an optical piece which effectively limits the diameter of an incident beam of light to produce an emerging beam of light with a desired cross sectional diameter.
Referring to FIG. 11, a conventional data imprinting device 10 imprints and superposes data on a film F. Data imprinting device 10 includes a data imprinting printed wired board (PWB) 13 located in an upper portion of a camera body 11. A plurality of light emitting elements 15, such as a row of light emitting diodes, is disposed on a lower surface of the data imprinting PWB 13. A driving circuit 17 to drive the light emitting elements 15 is also disposed on the lower surface of data imprinting PWB 13.
The camera body 11 has a first cavity 11a beneath the light emitting elements 15 for allowing the data imprinting light beams to travel through. A data imprinting optical piece 19 is disposed at the bottom of the first cavity 11a. The camera body 11 also has two additional cavities. A connecting cavity 11b has a reflecting member 21 fixed at the bottom thereof. Connecting cavity 11b links the first cavity 11a to a second cavity 11c extending perpendicular to the first cavity 11a and opening onto the film F.
Functionally, the illuminating light emanating from the light emitting elements 15 travels through the data imprinting optical piece 19. The light reflects off the reflecting member 21, and is focused through the second cavity 11c to the sensitive surface of the film F, generating the superposed data on the photographed picture.
The data imprinting device 10 uses a masking diaphragm 23 to block stray light L, which would otherwise impinge on a peripheral portion 19b. Masking diaphragm 23 sits above the upper surface of a peripheral portion 19b, integrally formed around a lens proper 19a of the data imprinting optical piece 19. The masking diaphragm 23 effectively controls the diameter of the incident beam of light.
Referring now to FIGS. 12 and 13, an upper surface 19d of the peripheral portion 19b is disposed perpendicular to an optical axis 19e of the lens proper 19a. In the absence of masking diaphragm 23, stray light L falling on the peripheral portion 19b is refracted therethrough into the lens proper 19a and further reaches the film F causing a flare, which results in degraded picture quality. Masking diaphragm 23 is therefore required to block the stray light L from impinging onto the peripheral portion 19b of the optical piece 19.
However, using the masking diaphragm 23 in the conventional data imprinting device 10 increases the production cost of the device. Another conventional method is to paint the upper surface 19d of the corresponding peripheral portion 19b with black pigment. However, this also does not eliminate the increased production costs.
A further method limits the beam diameter by the external periphery of the beam incident or emerging surfaces of the optical piece 19. A still further method limits the beam diameter by the internal periphery of the beam incident or emerging surface of the optical piece 19. These conventional methods for obtaining a main beam of light by controlling the diameter of an incident beam of light, do not sufficiently eliminate the effects of stray light L.
According to the further method, the external periphery defines the effective aperture. In other words, the entire incident or emerging surface serves as an effective aperture. However, this method has the following drawback. As shown in FIG. 14(a), a light beam falling within the effective aperture, but having a directional aberration with respect to the optical axis of the lens, hits the side wall of the lens, reflects off the side wall, and gives rise to ghosts. This occurs especially when the light beam falls on the part of the incident surface outside the effective aperture, since the beam tends to reach the side wall and thereby generates ghosts.
According to the still further method, the internal periphery defines the effective aperture. The part of the incident or emerging surface between the external and the internal peripheries is roughened or frosted so that the light rays falling outside the effective aperture are dispersed, suppressing flare components. However, this method also has a problem. As shown in FIG. 14(b), a light beam falling outside the effective aperture disperses when hitting the roughened or frosted area. The dispersion, however, only subdues flare components to a certain degree.
Referring to FIG. 14(c), another embodiment of the prior art employs a masking diaphragm about the perimeter of a lens, similar to the prior art embodiment in FIGS. 11-13. This embodiment does not have an upper portion corresponding to 19d in FIG. 13. This embodiment has the same, or worse, problems as the embodiment in FIGS. 11-13.